1. Field of the Invention
The present invention relates to an electrophotographic toner for use in electrophotographic apparatuses which utilize an electrophotographic process such as copying machines, printers, facsimiles, and the like, a production method thereof, an electrophotographic developer, and an image-forming process using the toner.
2. Description of the Related Art
Many electrophotographic methods are already known (see, for example, Japanese Patent Application Publication (JP-B) No. 42-23910). Generally, a fixed image is formed after undergoing the plural steps in which a latent image is electrostatically formed by various means on a surface of a photosensitive body (latent image carrier) which utilizes a photoconductive substance, the formed latent image is developed using electrophotographic toner (hereinafter, referred to as simply “toner”) to form a toner image, the toner image on the surface of the photosensitive body is transferred onto a surface of a recording material such as paper or the like, and this transferred image is fixed by compression or thermocompression and solvent vapor, etc. Toner remaining on the surface of the photosensitive body is cleaned, as required, by various methods and is again supplied for the aforementioned plural steps.
As a fixing technique for fixing a transfer image which has been transferred onto a surface of a recording material, a heat roll fixing method of inserting a transferable body onto which a toner image has been transferred between a pair of rolls composed of a heating roll and a pressure roll to fix the image is common. In addition, as a similar technique, a technique in which one or both of the rolls is substituted with a belt is also known. Compared to other fixing means, these techniques provide an image that is firmly fixed at high speed, have a high energy efficiency, and cause minimal damage to the environment due to volatilization of solvent or the like.
On the other hand, a technique for fixing toner using less energy is desired in order to reduce the amount of energy usage in copying machines and printers. For this reason, there is a strong demand for an electrophotographic toner which can be fixed at a lower temperature.
As a method of lowering the toner fixing temperature, a technique of lowering the glass transition point of a toner resin (binder resin) is commonly used. However, when the glass transition point is too low, since aggregation of powder (blocking) occurs easily and retainability of toner on the surface of a fixed image is lost, the lower limit in practical terms is 50° C. This glass transition point is a design feature of toner resins which are currently widely sold, and there has been a problem that in the methods for lowering the glass transition point it has not been possible to obtain a toner with a lower glass transition point than at present. In addition, although the fixing temperature can be lowered using a plasticizer, there have been problems of blocking occurring during storage of toner or in a developing device.
As a means for preventing blocking and realizing both image retainability up to 60° C. and low temperature fixability, a technique using a crystalline resin as a binder resin constituting a toner has been considered, and a method of using a crystalline resin as a toner for the purpose of realizing both blocking prevention and low temperature fixing has been long known (see, for example, JP-B No. 56-13943). In addition, for the purpose of offset prevention and compression fixing, a technique of using a crystalline resin has been long known (see, for example, JP-B Nos. 62-39428 and 63-25335).
However, when a crystalline resin is used alone, the strength of the crystalline resin is lower than that of amorphous resins and the crystalline resin has a problem of low powder reliability. In particular, problems of storage at a high temperature, blocking occurring in a developing device, and filming occurring on a photosensitive drum easily arise.
For improving the strength of binder resin, a method of mixing a crystalline resin and an amorphous resin was disclosed, and a toner comprising a crystalline polyester and an amorphous resin that does not have the crystalline resin in the surface layer has been proposed (e.g., Japanese Patent Application Laid-Open (JP-A) No. 2004-191927) in which it is possible to improve the low-temperature fixing efficiency and the image strength at the same time. However, in recent years, there is a need to obtain an image close to a photographic-quality image, i.e., an image having a higher glossiness such as that of gravure printing, even if low-temperature fixing is carried out, and the method above is still unsatisfactory for that purpose and needs to be improved.